Debugging Locally Installed Maven Dependencies in VS Code on Ubuntu

When working with Java projects in Visual Studio Code on Ubuntu, one common scenario developers face is debugging third-party Maven dependencies. Normally, Maven downloads dependencies from central repositories and uses compiled versions, providing little insight into their internal workings during debugging sessions. This scenario creates challenges when you need to debug or troubleshoot issues within the dependency itself. A practical workaround is configuring your project to use locally compiled dependencies, enabling detailed debugging and code modification directly within VS Code.

Setting Up Visual Studio Code for Java Development

If you haven’t already installed Visual Studio Code (VS Code) on your Ubuntu machine, it’s straightforward. Here’s how you can quickly get up and running:

• Open the terminal and add Microsoft’s official package repository:

wget -qO- https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > packages.microsoft.gpg
sudo install -D -o root -g root -m 644 packages.microsoft.gpg /usr/share/keyrings/packages.microsoft.gpg
sudo sh -c 'echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/packages.microsoft.gpg] https://packages.microsoft.com/repos/vscode stable main" > /etc/apt/sources.list.d/vscode.list'

• Install VS Code:

sudo apt update
sudo apt install code

Once VS Code is installed, you’ll want to set it up specifically for Java Development. Install the official Java Extension Pack by Microsoft through the extensions marketplace:

• Open VS Code, press Ctrl+Shift+X, search for “Java Extension Pack,” and install it.

This extension bundle includes everything you need, like Language Support for Java, Debugger, and Maven integrations.

Understanding Maven Dependencies

Maven is one of the most widely used Java build tools. It handles complex project management tasks, including dependency provisioning and build lifecycle management. Essentially, it saves developers from the hassle of manually downloading libraries.

Dependencies in Maven can be accessed from online sources like Maven Central or custom repositories. However, sometimes you might need to directly tweak or debug pieces of dependent code—especially if it’s causing unexpected issues. Official dependencies hosted online are precompiled binaries, making debugging problematic.

In contrast, locally installed dependencies involve downloading the dependency’s source, compiling it locally, and pointing your project to this self-built artifact, allowing full debugging and edit capabilities. This process is common among Java developers troubleshooting complex library issues or testing their modifications before contributing to open-source repositories.

Why Debugging Maven Dependencies in VS Code?

Debugging a typical Java project works smoothly with VS Code. You just set breakpoints, launch a debugging session, step through code, examine variables, and you’re set.

But here’s the catch—if the issue resides in an external library fetched from Maven Central, debugging won’t let you step into that dependency. Maven dependencies are downloaded as compiled JAR files, stripped of debugging symbols, limiting your visibility into their internal workings.

By cloning a dependency’s GitHub repository and configuring Maven to use this locally built JAR file instead, you regain complete control. This lets you step through the dependency’s code line-by-line in VS Code and debug as though it were your own project.

Cloning the GitHub Repository and Building Locally

Imagine you’re working with a hypothetical Java library, let’s call it “ExampleLib,” hosted publicly on GitHub. Here’s how you’d check it out locally to enable debugging:

• Open your terminal and clone the ExampleLib repository to your workspace folder:

git clone https://github.com/example-author/examplelib.git
cd examplelib

• After cloning, compile the code locally using Maven:

mvn clean install

The command compiles the library source code and places the generated JAR files into your local Maven repository (usually located at ~/.m2/repository). Now your local build is available to any project you configure to point there.

Editing Your Project’s pom.xml File to Use the Local Dependency

Next, you need to instruct your dependent project’s Maven configuration (pom.xml) to use this locally installed ExampleLib instead of fetching from an online repository. To accomplish this, ensure the locally built library’s version matches what your project expects.

Here’s how you update your pom.xml in your dependent project to resolve the dependency locally:

<dependency>
    <groupId>com.example</groupId>
    <artifactId>examplelib</artifactId>
    <version>1.2.3-SNAPSHOT</version> <!-- Match to your locally built version -->
</dependency>

Confirm this matches the version number you’ve compiled. Once saved, refresh your Maven project to resolve this dependency:

mvn clean compile

You should now see your own compiled library being pulled locally by Maven rather than remotely.

Debug Locally Installed Maven Dependency in VS Code

At this point, you’re fully set to debug your local Maven dependency. Now, open VS Code:

• Set breakpoints in the ExampleLib source code directly (wherever issues or testing points are identified).
• Ensure your dependent project referencing ExampleLib is open in VS Code as a workspace.
• Start a debugging session in VS Code by clicking the debug icon and running your project’s main class or unit tests.

VS Code will dynamically load the debugging information from your locally compiled dependency. Any breakpoint, variable inspection, and stepping through lines of code is now fully accessible, significantly facilitating rapid debugging and troubleshooting.

You can even edit the source files in your locally compiled dependency directly, rebuild quickly, and immediately retest your adjustments. Simply recompile the library with:

mvn clean install

And then restart your debug session in VS Code to test the changes.

The Advantages of Debugging Local Maven Dependencies

Debugging and editing locally built dependencies have some clear benefits:

• Granular Debugging: Step through third-party dependency code seamlessly, leading to faster issue identification.
• Testing Improvements: Quickly prototype fixes directly inside dependent libraries without waiting for upstream maintainers to patch bugs or features.
• Understanding Internals: Helps efficiently learn how sophisticated libraries work internally, enhancing your understanding and adaptability as a developer.

Once confident that your adjustments are stable, consider contributing these fixes upstream. This helps the broader community and establishes you as an active, relevant open-source contributor.

Good Practices & Future Considerations

While this method provides great debugging power, handle it responsibly:

• Avoid long-term dependency on locally altered libraries: Make efforts to upstream important changes or create your custom fork to maintain compatibility and ease releases.
• Keep track of your customizations: Clearly document any local modifications to avoid confusion during future troubleshooting and codebase sharing.

Debugging locally provided Maven dependencies in VS Code might initially appear complex, but the benefits far outweigh the setup effort. Incorporating this technique into your Java workflow can significantly accelerate development and dramatically boost your debugging efficiency.

Have you encountered specific issues debugging Maven dependencies before? Feel free to share your experiences and tips in the comments! Let’s make Java debugging easier together.